= About removing cataracts =

[Ralph S]

Here's another question regarding not reintroducing a bonding material between the tube faceplate and the now-clean "safety glass": If most of you who have performed de-cat procedures don't replace the old PVA with something, but leave an air gap between the two, what's the point of reattaching the old front glass? Is it to maintain the extended radius of the tube face as it was when it left the factory and therefore fit the metal tube mask of the front shroud better or does it really matter in regards to this fit? Otherwise the whole reattachment process seems pointless given that the notion of "safety glass" has been defeated by leaving out the glue that makes safety glass work.

[old_tv_nut]

Originally Posted by Ralph S

...Otherwise the whole reattachment process seems pointless given that the notion of "safety glass" has been defeated by leaving out the glue that makes safety glass work.

The safety glass still provides a first line of impact resistance, and definitely protects against scratches of the tube itself, which would weaken it. How much strength is added by transferring force through the filler to the tube itself is not clear, but I think it is preferable to have the safety glass with an air gap compared to no safety glass at all.

It does seem likely that the greatest amount of impact resistance is from the tube itself, which is under compression from atmospheric pressure. I believe implosion requires that a sufficient uneven force or tension be developed in some part of the tube.

[marty59]

Originally Posted by Ralph S

Here's another question regarding not reintroducing a bonding material between the tube faceplate and the now-clean "safety glass": If most of you who have performed de-cat procedures don't replace the old PVA with something, but leave an air gap between the two, what's the point of reattaching the old front glass? Is it to maintain the extended radius of the tube face as it was when it left the factory and therefore fit the metal tube mask of the front shroud better or does it really matter in regards to this fit? Otherwise the whole reattachment process seems pointless given that the notion of "safety glass" has been defeated by leaving out the glue that makes safety glass work.

Ralph, a 21FBP22 is the same tube, or "bulb" with a different style glass in front and not bonded. I can say that it's safety glass will be thicker over the bonded types though.

A little more to your point though is that the tube will bolt in as there is no "precision tolerance" in it's mounting and look good.

And re-attaching the face does keep that original appearence and protect the "bulb" from getting scratched as mentioned. At least you can replace the front again if you need to and not risk any damage to the tube itself should something happen.

[nasadowsk]

Ok - the tube I'm soaking is coming along nicely. The faceplate (but not the tube!) cracked (mechanical stresses from the clothespins being a bit enthusiastically applied), and I pulled most of the pieces off. The remainder is soaking, but water seems to make slow but sure inroads into it.

What the heck is this stuff? After soaking, at ambient temperature (55-60 degrees, it's very brittle and not exactly clear. I'm guessing water leeched out the plasticizers from it. It's about 1/16th inch thick. Along the sheets of stuff I've broken off, they're pockmarked with areas where it decayed in advance.

What causes the decay? Possible hint:This tube came from a water-damaged box. Moisture ingress? But that doesn't explain the decay towards the center. Maybe it's an unstable compound - but I've got two RCA tubes that show virtually no sign of delamination (I think this tube's an RCA, too).

Everyone calls it PVA - have we gotten a confirmation that it actually *is* PVA?

Oh yeah, it burns really sooty and is pretty self sustaining once it gets going. Heat softens it up a lot. I tried acetone - no effect.

Is this stuff perhaps really a silicone of some sort? RTV, maybe?

[sampson159]

many crt rebuilders left off the safety glass.i think channel master installed them.i dont care for the safety glass myself.some were so thick that it made the picture look out of focus.i have a nos rca hi lite that was never installed.jigged it up and it is awesome.this is being saved for something special like maybe a combo.the glass is slighly tinted and the picture is stunning

[old_tv_nut]

Originally Posted by sampson159

...some were so thick that it made the picture look out of focus...

Are you thinking about the deliberately etched tubes? They had a texture to diffuse reflections, but it did soften the picture a bit.

[ChrisW6ATV]

I like the non-glare finish of the safety glass on the 21FJP22s, so that is one reason I would always reinstall it on any CRTs that I clean.

[nasadowsk]

My CRT is coming along After a few weeks of soaking, I've removed most of the broken faceplate, save for a few pieces.

I took a pealed off piece and experimented. Acetone tends to soften the stuff pretty well. I soaked the remainder of the tube in acetone and this netted the softening of the bonding agent. A putty knife could dig out, and even better, dig between the agent and the glass, breaking the seal. I removed a few large pieces, leaving one piece (which doesn't want to be a team player), stuck to the glass. it's soaking now, and hopefully by tomorrow afternoon it'll have absorbed some acetone and softened to the point where I can get a putty knife in to break the seal and peel it off. Once it's gone, I'll wipe the tube and put it into my Zenith, where it belongs....